Certain switches require a thin body (e.g. bushing) having a movable portion coupled into and rigidly affixed to a housing (sometimes referred to as an enclosure). Assembly of such switches generally requires a welding operation to affix the thin body to an opening in the enclosure adapted for receiving the body. In some applications, the body and the housing need to be maintained at a substantially sealed level to permit proper operation. Having the body and housing substantially sealed prevents ingress of environmental factors that can cause failure of the switch to properly conduct an electrical signal, such as due to corrosion.
As known in the art, the body is inserted into an opening in a flat top portion of the housing to reach an o-ring which allows a seal to be formed. A welding operation then follows which removes material from the thin body and/or the housing to bond the respective components to one another.
Known weld techniques, such as tungsten inert gas (TIG) welding, generally involve the arc being directed at the flat top surface of the housing in an attempt to push or splatter molten material on to the wall of the bushing to create a weld. Without a well defined target it was found by the present inventors that frequently excessive weld arc energy was inadvertently applied directly to the thin wall of the bushing, and a high level of operator skill was required to obtain acceptable welds that did not compromise the seal integrity of the switch.
For example, during assembly of sealed plunger limit switches, poor yield can occur due to product failing the environmental seal test which tests for seal integrity. One requirement imposed for such switches in certain applications, such as for monitoring whether and to what extent cockpit door is ajar, is the military specification, that being ≦10−6 cm3/sec for the leak rate. The cause for these leaks has been traced by the present inventors to generally be holes or excessively thin regions in the body created in the thin bushing walls during welding of a housing to the bushing. What is needed is switches having a new thin body or housing arrangement and related process that is less operator dependent and thus more manufacturable that better preserves the seal integrity of the switches.